Tunguska event

extinction

Red Queen hypothesis

Species have a large amount of variation - but their genetic resources are finite
Environment never stops changing
Eventually even the most varied gene pool will be exhausted, species goes extinct [all species doomed]
Van Valen

regression (sea level)

kill curve

plots the probability of percentage of species killed in a mass extinction event over time
use a "kill curve" to predict:
1) Likelihood of major extinction events
2) Average waiting time between mass extinctions

comet

asteroid

solid balls of rocks, high metal content
Orbits take them throughout the solar system
Most are located in the asteroid belt, between Mars and Jupiter. May be the remains of a planet that did not coalesce when the solar system formed
Asteroids are 30 feet or larger (10 m),

meteoroid (meteor)

meteorite

periodic extinction

every 26 million years, impacts have high periodicity attributable to four causes:
1) Planet X
2) Nemesis
3) Vertical oscillations of solar system through the plane of the Milky Way
4) Passing through the spiral arms of the galaxy as the solar system orbits galactic core. All either unlikely or not compatable with data.

Nemesis

The Great Dying

Permian extinction event
Devastation was truly profound
Estimated 52% of all families, 90-95% of all species on Earth went extinct in a relatively short period of time
Extinctions affected big and small, aquatic or terrestrial